Directory of Mark Twain's maxims, quotations, and various opinions:

PRACTICAL JOKES

When grown-up persons indulge in practical jokes, the fact gauges them.
They have lived narrow, obscure, and ignorant lives, and at full manhood
they still retain and cherish a job-lot of left-over standards and ideals
that would have been discarded with their boyhood if they had then moved
out into the world and a broader life.
- Mark Twain's Own Autobiography (from North American Review,
Feb. 1, 1907)